In the modern communication systems, there is an ever-increasing demand for smaller and more versatile portable terminals such as hand-portable telephones. It is known that the size of an antenna is a factor related to its performance. In addition, the interaction between antenna, telephone body and proximate environment (such as the user) must be considered when designing an antenna device. Moreover, there is often a requirement that two or more frequency bands be supported, further adding to the complexity of the design of antenna devices. It is thus becoming an increasing difficult task to manufacture such compact and versatile terminals, which exhibit good antenna performance under a variety of conditions.
In addition to the considerations discussed above, one must consider the fact that the radiating properties of an antenna device for a small-sized structure (such as a hand-held wireless radio communications device) depend heavily on the shape and size of the support structure. The support may include for example, a printed circuit board (PCB) of the device and terminal casing. All radiation properties, such as resonance frequency, input impedance, bandwidth, radiation pattern, gain, polarization, and near-field pattern are a product of the antenna device itself and its interaction with the PCB and the telephone casing. Thus, all references to radiation properties made below are intended to be for the whole device in which the antenna is incorporated.
Finally, when designing and manufacturing a terminal (hand-portable telephone) today, the antenna is commonly adapted to the characteristics of this specific terminal and to be suited for a particular use in a particular environment. Accordingly, the antenna device cannot be adapted to any specific condition under which a certain terminal is to be used, or for use with multiple terminal types. Thus, each terminal model must be provided with a specifically designed antenna, which normally cannot be optionally used in any other terminal type.
Receiving antennas, with diversity functionality, which can adapt to various radio wave environments, are known. Such diversity functionality systems may be used to suppress noise, and/or undesired signals such as delayed signals, which may cause inter-symbol interference, and co-channel interfering signals, and thus improve the signal quality. However, these diversity functioning antennas require complex receiver circuitry structure, including multiple receiver chains, and a plurality of antenna input ports.
Switchable antennas are known in the literature for achieving diversity. In such switchable antennas, certain characteristics of the antenna system can be varied by connecting/disconnecting segments of the dipole arms to make them longer or shorter, for instance.
However, none of the above arrangements provide any switchable antenna elements that are connected or disconnected on some intelligent basis, e.g. when needed due to signal conditions.